Today a substantial amount of cargo is shipped around the globe using large naval vessels or ships capable of traveling long distances over open sea.
When shipping bulk cargo or load, such as coal or ore, large bulk naval vessels or ships dedicated for loading bulk cargo are commonly used due to their capability of loading bulk cargo. Bulk vessels are commonly equipped with large cargo holds which are covered by some form of hatch or cover which is opened during loading and unloading of the cargo concerned. When handling bulk cargo, cranes equipped with buckets or similar are commonly used to handle the cargo.
Due to the substantial size of the bulk vessels used for long distance shipments, large harbor constructions or long piers are needed to ensure a sufficient depth enabling the vessels to moor during loading and unloading of cargo.
Infrastructures, such as harbors or piers are very costly to build and to maintain. Given this, it is today common to transload cargo from less sophisticated harbors, having a limited depth, to large naval vessels or ships used for long distance shipping.
The harbors used in case of transloading may even be temporary harbors or piers offering only a few meters of depth. Such temporary harbors or piers are commonly constructed in proximity to ore or coal deposits from which bulk cargo in form of ore or coal is to be shipped over long distances.
During the transloading of the bulk cargo, e.g. ore or coal, to the large naval vessel or ship it is common to use a number of barges, so called feeder barges, for carrying the cargo from the harbor to the large naval vessel. The barges are commonly simple open, often un-motorized, boats typically carrying 6000-10000 tons of cargo. The barges are commonly loaded with the bulk cargo using land based equipment such as cranes or dump trucks. After having been loaded, the barges are pulled or propelled to the large naval vessel or ship onto which the bulk cargo is going to be loaded. The loading of the large naval vessel or ship often takes place 5-8 nautical miles ashore, where the large naval vessel or ship is anchored during the loading.
In order to unload the cargo from a barge and load it onto the large naval vessel so called transloaders are commonly used. The transloaders used are motorized barges equipped with a crane used to transfer the cargo from the feeder barge or cargo carrying barge to the large naval vessel. The crane of the transloader is commonly rotatable and has a crane arm whose luffing angle is adjustable so as to be able to handle cargo at different distances from the crane itself.
The transloader may also be referred to as a barge, a crane barge, a floating crane, a floating cargo crane etc. Transloaders used today are typically about 70 m long and 25 m wide and is equipped with a crane capable of hoisting 30-50 tons.
FIG. 1 schematically illustrates a cross sectional view of a transloader according to prior art during transloading of cargo. The transloader is equipped with a centrally located crane. The transloader is illustrated during transfer of cargo where the transloader is positioned between the large naval vessel, shown to the left in the figure, and the barge carrying the cargo, shown to the right in the figure. Hence, the crane of the transloader can hoist cargo from the cargo carrying barge onto the large naval vessel or vice versa. The crane is shown in two working positions (one of which is shown with dotted lines), where the bucket of the crane is located at a centre of the cargo carrying barge and at a centre of the large naval vessel, respectively.
The hoisting of cargo brings about that the transloader is subjected to a large tilting momentum which will result in that the transloader is rolled, i.e. tilted sideways. A too large roll angle will bring about difficulties in operating the crane and will also render the security questionable. Too large rolling angles will consequently render the transloader unusable.
To address the problem of rolling caused by the tilting momentum of the crane, it is common practice to arrange a counterweight on the crane itself. The counterweight is commonly placed in an elevated position on a tower or pedestal on which the crane itself is positioned and is arranged to co-rotate with the crane such that the counterweight is always located on a side of the crane being opposite to the hoisting side. A counterweight in an elevated position does however bring about stability issues due to the increased height of the mass center of the transloader.
JPS-53108075-U suggests using a movable counterweight located below deck on a floating crane in order to counteract rolling of the floating crane. The counterweight may be moved to a starboard side and a port side so as to compensate for tilting momentums related to the operation of the crane.
As discussed above, the cargo which is being transloaded is retrieved from the cargo carrying barge by means of e.g. a bucket and dropped into a cargo load compartment on the large naval vessel. During the transloading procedure the luffing angle of the crane of FIG. 1 has to be adjusted as is shown in FIG. 1. The crane arm will have to be raised when retrieving cargo from the cargo carrying barge, mainly due to the fact that the cargo carrying barge is narrower than the large naval vessel. In other words, the crane arm of FIG. 1 will have to be raised to retrieve cargo from a central position of the narrow cargo carrying barge and subsequently be lowered to reach a central position of the large naval vessel in order to drop of cargo here.
Hence, the luffing angle of the care arm will have to be adjusted such that the cargo in average is retrieved closer to the crane than it is being dropped off onto the large naval vessel. Crane operation including adjustment of the luffing angle is time consuming bringing about a reduced overall capacity of the transloader.
Lloyd Damen Shipyard: “Damen CBA 6324 bulk cargo or container crane barge”, Transshipment of bulk cargoes and containers CLASS NOTATION Remote controlled Grab CONTAINER EQUIPMENT, 16 Jan. 2013, XP055144599, discloses a bulk cargo or container crane barge employed with a crane being located off centre with regard to a longitudinal centre axis of the crane barge. The crane barge is employed with a counterweight arrangement having a counterweight being positioned in an elevated position on a crane pedestal. The counter weight co-rotates with the crane, when the carne is rotated.
Hence, there is a need for an improved transloader having an increased capacity.